The goal of the research is to characterize the biological activity of functional mutants of the human rasH oncogene, and to identify the biochemical properties of the rasH protein important for neoplastic transformation. Recently developed structural and functional mutants of normal and activated rasH genes will be introduced into a variety of cell types. Included among these mutants are rasH proteins that are deficient in the binding or hydrolysis of guanine nucleotides. Using mutants of the activated rasH gene, the structural and biochemical properties of the rasH protein which are required for the transformation and tumorigenicity of fibroblasts and epithelial cells will be compared. In vitro cell systems will be established to assay the effects of rasH expression on cellular differentiation, and the rasH protein domains which function in differentiation will be characterized. Finally, in vitro random mutagenesis will be used to generate additional rasH mutants active in the transformation of epithelial cells, and in altering cellular differentiation.